Pumps and methods of pumping fluids into a well bore

ABSTRACT

A pump for pumping fluid down a well bore in a rock formation comprises: intake and discharge passages; a pumping chamber with a plunger therein; intake and discharge valve assemblies in the intake passage and the discharge passages. At least one valve assembly has a valve body movable into sealing contact with the valve seat by fluid pressure in the pumping chamber. The valve seat may have a cylindrical outer surface for mating reception in said intake passage, and a shoulder with a radially-projecting surface biased against a wall for sealing. A cushioning member may be interposed between the valve body and the valve seat. A seal may be interposed between said valve body and said valve seat, and configured so that between 35% and 60% of a sealing surface of said valve seat contacts the valve body.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application Nos. 62/087,018, 62/113,782 and 62/193,933, the entire contents of which are incorporated herein by reference.

FIELD

This relates to pumps for pumping pressurized fluids down well bores, and in particular, to fluid ends of such pumps.

BACKGROUND

Many well operations require pumping of fluids at very high pressures. For example, some wells are formed in rock formations. Completion of such wells may involve pumping of a fluid into the formation through a well bore at high pressure. Such pumping may cause cracking or expansion of cracks in the formation, which may release hydrocarbons for later extraction. Moreover, pumps may be used to pump cement down a well bore to complete the well bore casing, or to pump other fluids, such as acids, down the well bore.

In such pumps, the term “fluid end” is typically used to refer to the components that are in direct contact with fluid being pumped. A fluid end may be driven by a power end, such as a diesel or electric motor.

Down-hole pumping operations may require very high pumping pressures. For example, hydraulic fracturing may require pressures of many thousands of pounds per square inch (psi). High pumping pressures subject fluid end components to enormous stresses. Such stresses may cause fatigue and failure of components, requiring costly and time-consuming maintenance.

SUMMARY

An example pump for pumping fluid down a well bore in a rock formation comprises: an intake passage in communication with a fluid reservoir; a discharge passage in communication with the well bore in the rock formation; a pumping chamber with a plunger received therein for pumping fluid from the reservoir to the well bore by reciprocation of the plunger; intake and discharge valve assemblies in the intake passage and the discharge passage, respectively, for selectively sealing the intake and discharge passages, at least one of the intake and discharge valve assemblies comprising a valve body and a valve seat, the valve body movable into sealing contact with the valve seat by fluid pressure; a cushioning member interposed between the valve body and the valve seat.

Another example pump for pumping fluid down a well bore in a rock formation, comprises: an intake passage in communication with a fluid reservoir; a discharge passage in communication with the well bore in the rock formation; a pumping chamber with a plunger received therein for pumping fluid from the reservoir to the well bore by reciprocation of the plunger; intake and discharge valve assemblies in the intake passage and the discharge passage, respectively, for selectively sealing the intake and discharge passages, at least one of the intake and discharge valve assemblies comprising a valve body and a valve seat; the valve body movable by fluid pressure into sealing contact with the valve seat; the valve seat having a cylindrical outer surface for mating reception in the intake passage, and a shoulder with a radially-projecting surface biased against a wall of the intake passage by pressure in the pumping chamber, for sealing therewith.

Another example pump for pumping fluid down a well bore in a rock formation, comprises: an intake passage in communication with a fluid reservoir; a discharge passage in communication with the well bore in the rock formation; a pumping chamber with a plunger received therein for pumping fluid from the reservoir to the well bore by reciprocation of the plunger; intake and discharge valve assemblies in the intake passage and the discharge passage, respectively, for selectively sealing the intake and discharge passages, at least one of the intake and discharge valve assemblies comprising a valve body and a valve seat; the valve body movable by fluid pressure into sealing contact with the valve seat; a compressible seal positioned about the perimeter of the valve body and interposed between the valve body and the valve seat, the compressible seal configured so that, with the valve body in sealing contact with the valve seat, between 35% and 60% of a sealing surface of the valve seat is in contact with the valve body.

An example method of pumping fluid into a wellbore comprises, using a pump as disclosed herein: drawing a fluid through an intake valve of the pump by moving said plunger through an intake stroke; moving said plunger through a discharge stroke, thereby pressurizing fluid in said chamber, closing said intake valve and opening said discharge valve and forcing said fluid through said discharge valve into said wellbore.

BRIEF DESCRIPTION OF DRAWINGS

In the drawings which illustrate, by way of example only, embodiments of the invention:

FIG. 1 is a schematic view of a well bore in a rock formation;

FIG. 2 is a perspective view of a pump fluid end, with a housing thereof partially cut away;

FIG. 3 is a cross-sectional view of the pump fluid end of FIG. 2;

FIG. 4 is a cross-sectional view of a valve assembly;

FIG. 5 is a cross-sectional view of another valve assembly;

FIG. 6 is a cross-sectional view of another valve assembly;

FIG. 7 is a cross-sectional view of another valve assembly;

FIG. 8 is a cross-sectional view of another valve assembly;

FIG. 9 is a cross-sectional view of another valve assembly;

FIG. 10 is a cross-sectional view of another valve assembly; and

FIG. 11 is a cross-sectional view of another valve assembly.

DETAILED DESCRIPTION

FIG. 1 shows a schematic view of a well bore 100 drilled through a rock formation 102. Rock formation 102 may be a shale formation, or another suitable formation for creation of an oil well by hydraulic fracturing.

A pump 104 may be provided for pumping a pressurized fluid down the well bore 100. For example, as depicted, pump 104 may be used for hydraulic fracturing. In other embodiments, pump 104 may be used for other down-hole pumping, such as cement pumping for completing a well bore casing or acid pumping for cleaning components.

Down-hole pumping may require high-pressure fluids. Accordingly pump 104 may be intended to operate at very high pressures. For example, pump 104 may drive a fluid into well bore 100 at pressures up to many thousands of pounds per square inch (psi), forcing the fluid to create or widen cracks 108 in formation 102. Typically, pump 104 may operate at discharge pressures of 5,000-15,000 psi.

The fluid pumped into well bore 100 may be a suitable liquid, such as water, mixed with a proppant such as sand. The proppant may be forced into cracks 108 along with pressurized water and remain in the cracks after water is withdrawn, to maintain widening of the cracks. As used herein, the combination of injected liquid and proppant may be referred to as the fracturing fluid.

Pump 104 may comprise a fluid end 110 and a power end, namely, motor 112. Motor 112 may drive a plunger within fluid end 110 in a reciprocating motion to pump fracturing mixture. Motor 112 may be, for example, an internal-combustion engine, such as a diesel-fuelled engine, or an electric motor. Other suitable types of motor will be apparent to skilled persons. Motor 112 may drive fluid end 110 by a crankshaft 111. Motor 112 may be connected with a geartrain, for example, to provide for operation of motor 112 and fluid end 110 at different rotational speeds or to convert rotary motion to linear reciprocating motion.

FIG. 2 shows fluid end 110 in greater detail. Fluid end 110 has a housing 114, which may be a cast metal block with a machined plunger bore 116, intake passage 118 and discharge passage 120. Housing 114 may be formed from carbon steel, stainless steel or another material suitable to withstand high pressures.

Intake passage 118 communicates with a fracturing fluid reservoir 117, and discharge passage communicates through an outlet 119 (FIG. 3) with a pipe 121 (FIG. 1) leading to well bore 100. A blending pump (not shown) may be positioned upstream of intake passage 118. The blending pump may mix liquid and proppant in the fracturing fluid and may pressurize the fracturing fluid. As depicted in FIG. 2, housing 114 is partially cut away for the sake of illustration of bores 116, 118, 120 and components housed therein.

A plunger 122 is received in plunger bore 116. Plunger 122 may be formed from steel and may be mounted to a crankshaft (not shown) driven by motor 112 to move plunger 122 in a reciprocating back-and-forth motion within plunger bore 116. Reciprocating motion of plunger 122 draws fracturing fluid through intake bore 118 and into chamber 124 and then expels fracturing fluid through discharge passage 120 and into well bore 100. In other embodiments, plunger 122 may be replaced with a steel piston, which may be of reinforced construction suitable to withstand high pressures experienced in fluid end 110.

FIG. 2 depicts one plunger bore 116, one intake passage 118 and one discharge passage 120. However, fluid end 110 may have a plurality of plunger bores 116, each with an associated intake passage 118 and discharge passage 120. In an example, a fluid end 110 may have five sets of plunger bores 116, intake passages 118 and discharge passages 120, which may be aligned side-by-side with one another within a common housing 114.

FIG. 3 depicts a cross-sectional view of fluid end 100. As noted, plunger 122 is slidably received within plunger bore 116. Plunger 122 and plunger bore 116 engage one another to form a fluid-tight seal. Plunger 122 is slidable within plunger bore 116. Thus, plunger 122 and plunger bore 116 form a positive-displacement pump. Movement of plunger 122 in a first direction, indicated by arrow I in FIG. 3 (herein referred to as an intake stroke of plunger 122), draws fluid through intake passage 118 into a pumping chamber 124 at the end of plunger bore 116. Movement of plunger 122 in a second direction, indicated by arrow D in FIG. 3 (herein referred to as a discharge stroke of plunger 122), forces fluid out of pumping chamber 124 and through an outlet 119 of discharge passage 120 and out of fluid end 110. Plunger bore 116 and outlet passage 120 may have stoppers 123 sealing one end thereof. Stoppers 123 may be metal (e.g. steel) and may be threaded to housing 114. Optionally, stoppers 123 may include one or more elastomeric sealing member (e.g. o-rings or gaskets).

An intake valve assembly 126 is received in intake passage 118 and a discharge valve assembly 128 (FIG. 2) is received in discharge passage 120.

Each of intake valve assembly 126 and discharge valve assembly 128 has a valve body 130, a valve seat 132 and a perimeter seal 134.

Valve seat 132 has an inner bore 136 and a frustoconical sealing surface 138. Valve body 130 is received in inner bore 136 and has a plurality of arms 140 extending into contact with valve seat 132 to center valve body 130 within inner bore 136.

Perimeter seal 134 is received in an annular channel 142 extending around the underside of valve body 130. As used herein, references to the “upper” or “top” side or surface of valve body 130 refer to the surface of valve body 130 facing away from valve seat 132. References to the “lower”, “bottom” or “under” side or surface of valve body 130 refer to the surface facing towards valve body 130.

Valve body 130 and perimeter seal 134 define frustoconical sealing surfaces 142, 144, respectively, facing sealing surface 138 of valve seat 132. Sealing surface 138 and sealing surfaces 142 and 144 have complementary shapes for cooperatively forming a fluid-tight seal.

Valve body 130 is movable away from valve seat 132 (direction θ in FIG. 3) to an open position, and towards valve seat 132 (direction C in FIG. 3) to a closed position. As depicted in FIG. 3, valve body 130 of discharge valve assembly 128 is in its open position and valve body 130 of intake valve assembly 126 is in its closed position.

Valve body 130 and valve seat 132 may, for example, be formed from steel or another suitably strong metallic or non-metallic material. Perimeter seal 134 may, for example, be formed from elastomeric polyurethane or another resilient and durable elastomer capable of withstanding abrasion and stress due to high pressure flow.

In the open position, a passage 146 is formed between valve seat 132 and valve body 130 to permit fluid flow. In the closed position, sealing surfaces 142, 144 of valve body 130 and perimeter seal 132 are urged against sealing surface 138 of valve seat 132.

Each valve body may be biased towards its closed position by a spring such as a helical spring mounted in compression between a top surface of valve body 130 and an internal shoulder 148 defined in bore 118, 120.

Intake valve assembly 126 and discharge valve assembly 128 are pressure actuated. That is, high pressure in pumping chamber 124 relative to pressure outside fluid end 110 acts against the underside of valve body 130 of discharge valve assembly 128, causing it to open. Meanwhile, high pressure in pumping chamber 124 acts against the top surface of valve body 130 of intake valve assembly 126, forcing it closed.

Conversely, low pressure in pumping chamber 124 relative to the pressure outside fluid end 110 causes opening of valve body 130 of intake valve assembly 126 and closing of valve body 139 of discharge valve assembly 128.

In order to prevent fracturing fluid from leaking past valve assemblies 126, 128, each valve assembly may form a seal with the wall of intake passage 118 or discharge passage 120. As will be apparent, the seal must be robust in order to prevent leakage despite the high pressures experienced by fluid end 110.

Accordingly, with a valve seat 132 installed in intake passage 118 or discharge passage 120, outer wall 150 of the valve seat 132 matingly engages an inner wall 152 of the respective passage 118, 120. Outer wall 150 may be tapered in the closing direction of the valve assembly. Inner wall 152 may have a complementary taper. Thus, pressure on the top surface of valve body 130 urges tapered outer wall 150 into tight sealing engagement with tapered inner wall 152. Valve seat 132 may thus form a fluid-tight seal with passage 118/120, which may tend to be reinforced by application of pressure to close the valve assembly.

In operation, plunger 122 is driven by motor 112 through an alternating sequence of intake and discharge strokes. Each intake stroke causes a drop in pressure in pumping chamber 124 and each discharge stroke causes an increase in pressure in pumping chamber 124. During the intake stroke, pressure upstream of intake valve assembly 126 may be greater than the pressure in pumping chamber 124, causing intake valve assembly 126 to open. Fracturing fluid is drawn from reservoir 113 through intake passage 118 and into pumping chamber 124. At the end of an intake stroke, plunger 122 reverses direction to begin a discharge stroke. The discharge stroke causes an increase in pressure within pumping chamber 124. Elevated pressure in chamber 124 acts on the bottom surface of valve body 130 of discharge valve assembly 128, causing it to open so that fracturing fluid is forced out of fluid end 110 through pumping chamber 124 and discharge passage 120. At the same time, pressure in pumping chamber 124 acts on the top surface of valve body 130 of intake valve assembly 126, causing it to close.

As noted, the fracturing fluid may include a liquid, such as water, and a particulate proppant, such as sand or ceramic particles, suspended in the liquid. Accordingly, valve assemblies 126, 128 are configured to form seals even in the presence of particulates. As best shown in FIG. 3, sealing surface 144 of perimeter seal 134 extends downwardly past sealing surface 142 of valve body 130. Accordingly, when valve body 130 moves to its closed position, sealing surface 144 perimeter seal 134 contacts sealing surface 138 of valve seat 132 prior to sealing surface 142 of valve body 130 contacting sealing surface 138.

Perimeter seal 134 and valve seat 132 may therefore form an initial seal. When subjected to closing pressure, perimeter seal 134 may conform to any particulates present between sealing surfaces 144, 138. That is, perimeter seal 134 may deform to form a seal around such particulates.

After forming of an initial seal between perimeter seal 134 and valve seat 132, valve body may continue moving towards the closed position until its sealing surface 142 abuts and forms a seal with sealing surface 138.

In order for metal-to-metal contact between valve body 130 and valve seat 132 to occur, perimeter seal 134 may be compressed and deformed.

In order to widen cracks 108 in rock formation 102 (FIG. 1), plunger 122 may develop very high pressure. In an example, fluid end 110 may be rated for pressures of up to 15,000 psi within pumping chamber 124. At such pressure, during the discharge stroke of plunger 122, valve body 130 and valve seat 132 of intake valve assembly 126 may be subjected to forces of up to hundreds of thousands of pounds in the closing direction. Such forces may be borne by the interface between sealing surface 138 of valve seat 132 and each of sealing surface 142 of valve body 130 and sealing surface 144 of valve body 130. Valve seat 132 may in turn transfer forces to housing 114 of fluid end 110. In particular, the tapered sealing interface between outer wall 150 of valve seat 132 and inner wall 152 of intake passage 118 or discharge passage 120 may act as a wedge. That is, the tapered interface may convert stress exerted on valve body 130 into hoop and radial stresses around each of the intake passage 118 and discharge passage 120. Such hoop and radial stresses may be particularly high around intake passage 118 during the discharge stroke of plunger 122 and may frequently cause cracking or failure of housing 114 of fluid end 110.

As will be apparent, the fracturing fluid may be substantially incompressible. Accordingly, pressure in pumping chamber 124 may change rapidly when plunger 122 transitions from an intake stroke to a discharge stroke or vice-versa. Rapid increase of pressure in pumping chamber 124 at the beginning of a discharge stroke may cause valve body 130 of intake valve assembly 126 to rapidly move to its closed position. Due to the high pressure generated by plunger 122, along with the weight of the valve assembly and closing force imparted by the bias spring, acceleration of valve body 130 towards its closed position may be sufficient to cause significant impact between valve body 130 and valve seat 132. Such impact may impose further stress on one or both of valve body 130 and valve seat 132, which may cause deterioration or failure of either or both parts.

Accordingly, in some embodiments, valve assemblies 126, 128 may be provided with features for mitigating stress or wear.

FIG. 4 shows a cross-sectional view of an example valve assembly 160, which can be substituted for either of valve assemblies 126, 128. Valve assembly 160 has certain parts similar to those of valve assemblies 126, 128, and like parts are indicated with like reference characters. For example, valve body 130 and perimeter seal 134 of valve assembly 160 may be substantially identical to valve body 130 and perimeter seal 134 of valve assemblies 126, 128.

Valve assembly 160 has a valve seat 132′. Valve seat 132′ has an inner bore 136 and a generally frustoconical sealing surface 138′. An annular channel 162 may be formed in sealing surface 138′, and a cushioning member 164 may be received in channel 162.

Cushioning member 162 is interposed between valve body 130 and valve seat 132′ and is configured to decelerate valve body 130 as it approaches its closed position. Specifically, when pressure acts on the upper surface of valve body 130, pushing valve body 130 towards valve seat 132′, sealing surface 142 of valve body 130 contacts cushioning member 164 prior to contacting sealing surface 138 of valve seat 132′.

Cushioning member 164 may deform upon being contacted by valve body 130, absorbing energy from the valve body and decelerating the movement of the valve body. Such cushioning may mitigate stresses due to impact of valve body 130 on valve seat 132.

As depicted, cushioning member 164 is an elastomeric ring. Cushioning member 164 may be formed from a resilient elastomer. In some embodiments, the material of cushioning member 164 may be resistant to fatigue, such that cushioning member can be repeatedly compressed to absorb shock and return to its original shape. However, other suitable types of cushioning members may be used. For example, cushioning member 164 could be a helical spring seated in channel 162. Channel 162 may be configured so that cushioning member 164 can be compressed such that it is entirely received within channel 162. That is, when compressed, cushioning member 164 may not protrude from channel 162. When fully received within channel 162, cushioning member 164 may not interfere with sealing between metal sealing surface 142 of valve body, and metal sealing surface 138 of valve seat.

As depicted in FIG. 4, cushioning member 164 is received in a channel 162 formed in valve seat 132′. In other embodiments, a channel 162 may be formed in the underside of valve body 130 and cushioning member 164 received therein. For example, FIG. 5 depicts a valve assembly 160′ with a valve body 130 that has a channel 162 formed in its underside and a cushioning member 164 received therein.

In still other embodiments, channels may be formed in both of valve body 130 and valve seat 132 and cushioning members received in both channels. For example, FIG. 6 depicts a valve assembly 160″ including valve body 130′ with a first channel 162 a and cushioning member 162 b; and valve seat 132′ with a second channel 162 b and cushioning member 164 b. As depicted, cushioning members 164 a, 164 b are aligned so that they abut when valve body 130′ is in the closed position. However, in other embodiments, channels 162 a, 162 b and cushioning members 164 a, 164 b may be offset.

In some embodiments, cushioning member 164 may be a helical spring, for example, a metal spring. FIG. 7 depicts one such embodiment, in which valve assembly 160′″ has a helical spring cushioning member 164. Helical spring cushioning member 164 has a lower coil 163 received in a channel 162 a formed in the underside of valve body 130′, and an upper coil 165 received in a channel 162 b formed in valve seat 132′. When valve body 130′ is in its closed position, channels 162 a, 162 b abut one another and helical spring cushioning member 164 is compressed so that it is received entirely within channels 162 a, 162 b and sealing surfaces 138, 142 can engage and seal with one another.

In other embodiments, cushioning member 164 may be formed from other types of springs. For example, cushioning member 164 may be a Belleville washer.

FIG. 8 shows a cross-sectional view of another example valve assembly 170, which can be substituted for either of valve assemblies 126, 128. Valve assembly 170 has certain parts similar to those of valve assemblies 126, 128, and like parts are indicated with like reference characters. For example, valve body 130 and perimeter seal 134 of valve assembly 170 may be substantially identical to valve body 130 and perimeter seal of valve assemblies 126, 128.

Valve assembly 170 has a valve seat 172. Valve seat 172 has an inner bore 136 and a generally frustoconical sealing surface 138. Valve seat 172 further has an outer surface 174 and an outwardly (e.g. radially) projecting shoulder 176 with a radially-extending surface 177.

Unlike outer surface 150 of valve seat 132, outer surface 174 of valve seat 172 is cylindrical. That is, outer surface 174 does not taper. Valve seat 172 may be received in a bore defined in housing 114 with a surface 178 that is likewise cylindrical. The bore may have a shoulder with a radially-extending surface 179 opposing surface 177 of valve seat 172.

The cylindrical shape of surfaces 174, 178 may avoid the wedge effect and consequent hoop and radial stress associated with the tapered interface of surfaces 150, 152 (FIG. 3). When valve body 130 is forced into its closed position by pressure acting on the top surface of valve body 130, valve seat 172 with its cylindrical outer surface 174 may not transfer any radial or hoop stress to the housing in which it is received. Instead, force exerted on valve body 130 may be borne by radially-projecting shoulder 176. Force transferred to housing 114 may be along the length of the valve assembly, i.e. in the open-close direction, rather than in the radial direction. Housing 114 may be stronger in this direction, and force transferred from shoulder 176 to housing 114 may be less likely to cause cracking or failure of housing 114.

Since surfaces 174, 178 are cylindrical, rather than tapered, they may not engage one another as tightly as surfaces 150, 152 (FIG. 3) and therefore, may not form a metal-to-metal seal with one another. Rather, shoulder 176 may have an annular channel 180 facing housing 114, and a seal 182 may be received therein for sealing with the housing surface. As depicted, seal 182 may be an elastomeric ring. However, other configurations are possible.

As will be apparent, pressure exerted on the top surface of valve body 130 may result in valve seat 172 and thus, shoulder 176, being urged against housing 114. This may likewise bias seal 182 against the housing. Thus, high pressure acting on valve body 130 may tend to increase the integrity of the seal formed by seal 182.

In addition, valve seat 172 may have a second annular channel 184 formed in its circumferential face, opposing surface 178. A second seal 186 may be received within channel 184.

As noted above, when valve assemblies are subjected to pressure in their closed positions, perimeter seal 134 may be squeezed between the valve body and valve seat. In particular, perimeter seal 134 may be compressed. Perimeter seal 134 may also be subjected to shear stress. Such shear stress may tend to urge the perimeter seal 134 out of its channel in valve body 130, 130′.

Accordingly, as shown in FIG. 3, perimeter seal 134 may have a body 183 and an inwardly-projecting flange 186 received in channel 142. Flange 186 extends at an angle approximately perpendicular to sealing surface 144 of perimeter seal 134. When valve body 130, 130′ is in its sealing position, with sealing surface 144 urged against the sealing surface of the valve seat, flange 186 is pressed into channel 142. Pressing of flange 186 into channel 142 may resist deformation or displacement of perimeter seal.

As depicted in FIG. 3, valve body 130, perimeter seal 134 and annular channel 142 are configured such that sealing surface 138 partly seals with sealing surface 142 and partly seals with sealing surface 144. Regions in which sealing surface 142 directly contacts sealing surface 138 may be referred to as metal-elastomer regions. Regions in which sealing surface 144 directly contacts sealing surface 138 may be referred to as metal-metal regions. As depicted in FIG. 3, the area of sealing surface 142 may be approximately 0.9 times the area of sealing surface 144 and the area of sealing surface 142 may be approximately 0.34 times the area of sealing surface 138. Thus, metal-metal contact regions may occupy 34% of the area of sealing surface 138 and metal-elastomer contact regions may occupy approximately 40% of the area of sealing surface 138.

During sealing, perimeter seal 134 may be compressed until metal sealing surface 142 contacts sealing surface 138 of valve seat 132. Force associated with sealing may be borne entirely or in substantial part by the metal-metal interface between valve body 130 and valve seat 132. Perimeter seal 134 may experience stress, such as compressive or shear stress, which may be proportional to the amount of deformation of the metal-elastomer region. Stress on perimeter seal 134 may cause deterioration of perimeter seal 134, which may in turn lead to failure (e.g. leaking) of the valve assembly. In addition, valve body 130 and valve seat 132 may experience stress. Stress and or wearing of valve body 130, valve seat 132 or perimeter seal 134 may be inversely related to the area of the metal-metal interface between valve body 130 and valve seat 132 during sealing. In other words, increasing the area of metal-metal contact may limit stress on or wearing of valve body 130, valve seat 132 or perimeter seal 134.

Thus, in some embodiments, the valve body and perimeter seal may be configured to limit the size of the metal-elastomer contact area between the perimeter seal and the sealing surface of the valve seat (and correspondingly, to increase the size of the metal-metal contact area between valve body 130 and valve seat 132).

FIG. 9 shows one such example valve assembly 190. Valve assembly 190 has a valve body 192 and perimeter seal 194 configured to provide large metal-metal contact area, but is otherwise generally similar to valve assemblies 126, 128 and like components are identified with like reference characters.

Valve body 190 has an annular channel 196 extending around the periphery of its underside. Perimeter seal 194 has a body 198 and a flange 200 and is received in channel 196. Body 198 defines a sealing surface 202 for sealing against sealing surface 138 of valve seat 132. Body 198 is relatively smaller than body 183 (FIG. 3) and sealing surface 202 is likewise smaller than sealing surface 144. In the depicted example, the metal area of valve body sealing surface 142, may be approximately 8 square inches. The area of elastomer sealing surface 202 may be approximately 4.5 square inches. The area of valve seat sealing surface 138 may be approximately 16 square inches. Thus, the area of valve body sealing surface may be approximately half of the area of valve seat sealing surface 138. Accordingly, when the valve assembly is sealed, about half of the area of valve seat seating surface 138 may contact valve body 130. The area of elastomer sealing surface 202 may be approximately 28% of the area of valve seat sealing surface 138. Accordingly, when the valve assembly is sealed, about half of the area of valve seat seating surface 138 may contact perimeter seal 194.

In some embodiments, these sizes and ratios may vary. Typically, the area of sealing surface 142 of valve body 130 is between 35% and 60% of the area of sealing surface 138 of valve seat 132. Typically, the area of metal-to-metal contact is approximately 1.5 to 2.0 times the area of metal-to-elastomer sealing contact.

Flange 200 may have one or more retention notches 204 formed along its length. When perimeter seal 194 is installed to valve body 190, retention notches 204 may receive corresponding tabs 206 extending from a wall of channel 196. The shapes of notches 204 and tabs 206 may be such that reception of tabs 206 in notches 204 locks perimeter seal 194 in channel 196. Thus, tabs 206 and notches 204 may prevent egress of perimeter seal from channel 196 when valve body 190 is pressed against valve seat 132.

In other embodiments, notches 204 and tabs 206 may be omitted, in which case perimeter seal 194 may be retained in channel 196 by urging of flange 200 into channel 196 when perimeter seal 194 is compressed. FIG. 10 depicts such an embodiment, in which valve body 190 has a channel 196′ that is identical to channel 196 except that it lacks tabs 206. A perimeter seal 194′ is received in channel 196 and is identical to perimeter seal 194 except that it lacks notches 204.

In some embodiments, perimeter seal 194 may be bonded in channel 196 using an adhesive bonding agent. For example, a bonding agent may be applied to channel 196, and molten elastomer may be poured into channel 196. The molten elastomer may harden to form perimeter seal 194.

Perimeter seal 194 may be sized to deform between the valve and valve seat under pressure without allowing by-pass of fluid. For example, perimeter seal 194 may be sufficiently large to deform and form a seal around particulates suspended in the fluid pumped by fluid end 110.

In some embodiments, valve assemblies may include some or all of the features disclosed herein for mitigating stress and wear effects. For example, FIG. 11 depicts one such valve assembly 300. Valve assembly 300 includes a valve body 302 and a valve seat 304, the latter received in an intake or discharge passage in housing 114 of fluid end 110.

Valve body 302 has an inner bore 306 and an outer surface 308, and a sealing surface 310. Outer surface 308 is cylindrical and the passage of housing 114 in which it is received is likewise cylindrical. Valve seat 304 also has a radially-projecting flange 310 which bears against a radial shoulder defined by housing 114. A seal member 312 is disposed between flange 310 and the housing shoulder, to define a seal that is reinforced by pressure exerted on the top of valve body 302.

Sealing surface 308 of valve seat 304 has an annular channel 310, in which a cushioning member 312 is received to absorb energy from closing of valve assembly 300 and thereby limit impact stress on valve body 302 and valve seat 304. As depicted, cushioning member 312 is an elastomeric ring. However, cushioning member 312 may be any type of cushioning member as described above.

Valve seat 304 also has an annular channel 314 extending around the periphery of its underside, in which a perimeter seal 316 is received. Perimeter seal 316 and channel 314 are configured similarly to perimeter seal 194 and channel 196 discussed above. In particular, perimeter seal 316 has a body 318 and a flange 320 extending into channel 314 and is configured so that, when valve assembly 300 is closed, the area of metal-to-metal sealing contact between valve body 302 and valve seat 304 is approximately half of the area of sealing surface 310. Like perimeter seal 194 and channel 196, perimeter seal 316 and annular channel 314 have retention notches 322 and tabs 324 to lock perimeter seal 316 in annular channel 314.

Methods of pumping fluids down a well bore may be performed using pumps with valve assemblies as disclosed herein. For example, a fluid end may be provided, with one valve assembly 300 acting as an intake valve and one valve assembly acting as a discharge valve. Plunger 122 (FIG. 3) may be moved through an intake stroke to draw fluid from a reservoir through an intake valve assembly 300 and into pumping chamber 124. During the intake stroke, pressure differential across intake valve assembly 300 causes the intake valve assembly 300 to open and discharge valve assembly 300 to close.

Plunger 122 may be moved through a discharge stroke, which may pressurize fluid in pumping chamber 124. Positive pressure in chamber 124 may cause intake valve assembly 300 to close and discharge valve assembly 300 to open. Movement of plunger 122 likewise causes fluid to be forced through discharge valve assembly 300 and into well bore 100.

Just after the beginning of the intake stroke, pressure in chamber 124 drops such that pressure upstream of intake valve assembly 300 is greater than pressure downstream of intake valve assembly 300, which causes intake valve assembly 300 to open. Just after the beginning of the discharge stroke, pressure in chamber 124 rises, causing discharge valve assembly 300 to close. The pressures may change quickly, resulting in rapid movement of valve bodies 302. Valve bodies 302 may contact and compress cushioning members 312 and flange 310 may be urged against housing 114 to seal therewith.

The preceding discussion provides many example embodiments. Although each embodiment represents a single combination of inventive elements, other examples may include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, other remaining combinations of A, B, C, or D, may also be used.

Although the embodiments have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the scope as defined by the appended claims.

Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps

As can be understood, the examples described above and illustrated are intended to be exemplary only. The invention is defined by the claims. 

What is claimed is:
 1. A pump for pumping fluid down a well bore in a rock formation, comprising: an intake passage in communication with a fluid reservoir; a discharge passage in communication with said well bore in said rock formation; a pumping chamber with a plunger received therein for pumping fluid from said reservoir to said well bore by reciprocation of said plunger; intake and discharge valve assemblies in said intake passage and said discharge passage, respectively, for selectively sealing said intake and discharge passages, at least one of said intake and discharge valve assemblies comprising a valve body and a valve seat, said valve body movable into sealing contact with said valve seat by fluid pressure; a cushioning member interposed between said valve body and said valve seat.
 2. The pump of claim 1, wherein said valve body contacts said cushioning member prior to contacting said valve seat, thereby decelerating said valve body.
 3. The pump of claim 1, wherein said cushioning member comprises an elastomeric ring.
 4. The pump of claim 1, wherein said cushioning member comprises a spring.
 5. The pump of claim 1, wherein said cushioning member is received in a channel in said valve seat.
 6. The pump of claim 1, wherein said cushioning member is received in a channel in said valve body.
 7. The pump of claim 4, wherein, during sealing contact of said valve body and said valve seat, said cushioning member is compressed such that it does not protrude from said channel.
 8. The pump of claim 5, further comprising a second cushioning member received in a channel in said valve body.
 9. The pump of claim 1, wherein said valve seat has a cylindrical outer surface for mating reception in said intake passage, and a shoulder with a radially-projecting surface biased against a wall of said intake passage by pressure in said pumping chamber, for sealing therewith.
 10. The pump of claim 9, further comprising a compressible seal positioned about the perimeter of said valve body and interposed between said valve body and said valve seat, said compressible seal configured so that, with said valve body in sealing contact with said valve seat, between 35% and 60% of a sealing surface of said valve seat is in contact with said valve body.
 11. A pump for pumping fluid down a well bore in a rock formation, comprising: an intake passage in communication with a fluid reservoir; a discharge passage in communication with said well bore in said rock formation; a pumping chamber with a plunger received therein for pumping fluid from said reservoir to said well bore by reciprocation of said plunger; intake and discharge valve assemblies in said intake passage and said discharge passage, respectively, for selectively sealing said intake and discharge passages, at least one of said intake and discharge valve assemblies comprising a valve body and a valve seat; said valve body movable by fluid pressure into sealing contact with said valve seat; said valve seat having a cylindrical outer surface for mating reception in said intake passage or said discharge passage, and a shoulder with a radially-projecting surface biased against a wall of said passage by pressure in said pumping chamber, for sealing therewith.
 12. The pump of claim 11, further comprising a resilient seal member interposed between said radially-projecting shoulder and said wall of said intake or discharge passage.
 13. The pump of claim 12, further comprising a resilient seal member interposed between said cylindrical outer surface of said valve seat and a wall of said intake or discharge passage.
 14. The pump of claim 12, wherein said resilient seal member is received in a channel in said shoulder.
 15. The pump of claim 11, further comprising a compressible seal positioned about the perimeter of said valve body and interposed between said valve body and said valve seat, said compressible seal configured so that, with said valve body in sealing contact with said valve seat, between 35% and 60% of a sealing surface of said valve seat is in contact with said valve body.
 16. A pump for pumping fluid down a well bore in a rock formation, comprising: an intake passage in communication with a fluid reservoir; a discharge passage in communication with said well bore in said rock formation; a pumping chamber with a plunger received therein for pumping fluid from said reservoir to said well bore by reciprocation of said plunger; intake and discharge valve assemblies in said intake passage and said discharge passage, respectively, for selectively sealing said intake and discharge passages, said intake valve assembly comprising a valve body and a valve seat; said valve body movable by fluid pressure into sealing contact with said valve seat; a compressible seal positioned about the perimeter of said valve body and interposed between said valve body and said valve seat, said compressible seal configured so that, with said valve body in sealing contact with said valve seat, between 35% and 60% of a sealing surface of said valve seat is in contact with said valve body.
 17. The pump of claim 16, wherein said compressible seal is received in a channel defined in said valve body.
 18. The pump of claim 17, wherein said compressible seal has a notch for receiving a corresponding tab projecting from said valve body to lock said compressible seal in said channel.
 19. The pump of claim 16, further comprising a cushioning member interposed between said valve body and said valve seat.
 20. The pump of claim 1, wherein said pump is for hydraulic fracturing in said reservoir.
 21. The pump of claim 11, wherein said pump is for hydraulic fracturing in said reservoir.
 22. The pump of claim 16, wherein said pump is for hydraulic fracturing in said reservoir.
 23. A method of pumping fluid into a wellbore, comprising: drawing a fluid through an intake valve of the pump of claim 1 by moving said plunger through an intake stroke; moving said plunger through a discharge stroke, thereby pressurizing fluid in said chamber, closing said intake valve and opening said discharge valve and forcing said fluid through said discharge valve into said wellbore.
 24. A method of pumping fluid into a wellbore, comprising: drawing a fluid through an intake valve of the pump of claim 11 by moving said plunger through an intake stroke; moving said plunger through a discharge stroke, thereby pressurizing fluid in said chamber, closing said intake valve and opening said discharge valve and forcing said fluid through said discharge valve into said wellbore.
 25. A method of pumping fluid into a wellbore, comprising: drawing a fluid through an intake valve of the pump of claim 16 by moving said plunger through an intake stroke; moving said plunger through a discharge stroke, thereby pressurizing fluid in said chamber, closing said intake valve and opening said discharge valve and forcing said fluid through said discharge valve into said wellbore. 